Compressible fluid strut

ABSTRACT

A suspension strut ( 10 ) for a vehicle including a compressible fluid ( 20 ), a hydraulic tube ( 22,22 ′) and displacement rod ( 24 ) adapted to cooperate with the compressible fluid ( 20 ) to supply a suspending spring force that biases the wheel toward the surface, a cavity piston ( 26,26 ′) separating the inner cavity ( 30 ) into a first section ( 32 ) and a second section ( 34 ) and defining a first orifice ( 36 ) adapted to allow flow of the compressible fluid ( 20 ) between the first section ( 32 ) and the second section ( 34 ) of the inner cavity ( 30 ), and a first variable restrictor ( 28 ) adapted to variably restrict the passage of the compressible fluid ( 20 ) through the first orifice ( 36 ) based on the velocity of the cavity piston ( 26,26 ′) to the hydraulic tube ( 22,22 ′).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present this invention claims priority to U.S. provisionalapplication Serial No. 60/251,951, filed Dec. 7, 2000, entitled“Compressible Fluid Strut”.

TECHNICAL FIELD

[0002] The subject matter of this invention generally relates tosuspension struts for a vehicle and, more particularly, to suspensionstruts including a compressible fluid.

BACKGROUND OF THE INVENTION

[0003] In the typical vehicle, a combination of a coil spring and a gasstrut function to allow compression movement of a wheel toward thevehicle and rebound movement of the wheel toward the ground. Thesuspension struts attempt to provide isolation of the vehicle from theroughness of the road and resistance to the roll of the vehicle during aturn. More specifically, the typical coil spring provides a suspendingspring force that biases the wheel toward the ground and the typical gasstrut provides a damping force that dampens both the suspending springforce and any impact force imparted by the road. Inherent in everyconventional suspension strut is a compromise between ride (the abilityto isolate the vehicle from the road surface) and handling (the abilityto resist roll of the vehicle). Vehicles are typically engineered formaximum road isolation (found in the luxury market) or for maximum rollresistance (found in the sport car market). There is a need, however,for an improved suspension strut that avoids this inherent compromise.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004]FIG. 1 is a front view of a suspension strut of the preferredembodiment of the invention, shown within a vehicle.

[0005]FIG. 2 is a cross-sectional view of the suspension strut of thefirst preferred embodiment of the invention.

[0006]FIG. 3 is a cross-sectional view of a suspension strut of thesecond preferred embodiment of the invention.

[0007]FIG. 4 is a cross-sectional view of a suspension strut of thethird preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0008] The following description of the three embodiments of theinvention is not intended to limit the invention to these preferredembodiments, but rather to enable any person skilled in the art ofsuspension struts to use this invention.

[0009] As shown in FIG. 1, the suspension strut 10 of the invention hasbeen specifically designed for a vehicle 12 having a wheel 14 contactinga surface 16 under the vehicle 12 and a suspension link 18 suspendingthe wheel 14 from the vehicle 12. The suspension link 18 allowscompression movement of the wheel 14 toward the vehicle 12 and reboundmovement of the wheel 14 toward the surface 16. Despite its design for aparticular environment, the suspension strut 10 may be used in anysuitable environment.

[0010] As shown in FIG. 2, the suspension strut 10 of the firstpreferred embodiment includes a compressible fluid 20, a hydraulic tube22 and displacement rod 24, a cavity piston 26, and a first variablerestrictor 28. The hydraulic tube 22 and the compressible fluid 20cooperate to supply a suspending spring force that biases the wheeltoward the surface, while the cavity piston 26 and the first variablerestrictor 28 cooperate to supply a rebound damping force that dampensthe suspending spring force. The suspension strut 10, of course, mayinclude other components or systems that do not substantially interferewith the functions and purposes of these components.

[0011] The compressible fluid 20 of the first preferred embodiment,which cooperates to supply the suspending spring force, is preferably asilicon fluid that compresses about 1.5% volume at 2,000 psi, about 3%volume at 5,000 psi, and about 6% volume at 10,000 psi. Above 2,000 psi,the compressible fluid 20 has a larger compressibility than conventionalhydraulic oil. The compressible fluid 20, however, may alternatively beany suitable fluid, with or without a silicon component, that provides alarger compressibility above 2,000 psi than conventional hydraulic oil.

[0012] The hydraulic tube 22 and displacement rod 24 of the firstpreferred embodiment cooperatively function to couple the suspensionlink and the vehicle and to allow compression movement of the wheeltoward the vehicle and rebound movement of the wheel toward the surface.The hydraulic tube 22 preferably defines an inner cavity 30, whichfunctions to contain a portion of the compressible fluid 20. Aspreviously mentioned, the inner cavity 30 and the compressible fluid 20preferably cooperate to supply the suspending spring force that biasesthe wheel toward the surface, and essentially suspends the entirevehicle above the surface. The displacement rod 24 is adapted to moveinto the inner cavity 30 upon the compression movement of the wheel andto move out of the inner cavity 30 upon the rebound movement of thewheel. As it moves into the inner cavity 30, the displacement rod 24displaces, and thereby compresses, the compressible fluid 20. In thismanner, the movement of the displacement rod 24 into the inner cavity 30increases the suspending spring force of the suspension strut 10. As thedisplacement rod 24 moves out of the inner cavity 30, the compressiblefluid 20 decompresses and the suspending spring force of the suspensionstrut 10 decreases. The displacement rod 24 is preferably cylindricallyshaped and, because of this preference, the displacement of thedisplacement rod 24 within the inner cavity 30 and the magnitude of thesuspending spring force have a linear relationship. If a linearrelationship is not preferred for the particular application of thesuspension strut 10, or if there is any other appropriate reason, thedisplacement rod 24 may be alternatively designed with another suitableshape. The hydraulic tube 22 and the displacement rod 24 are preferablymade from conventional steel and with conventional methods, but mayalternatively be made from any suitable material and with any suitablemethod.

[0013] The cavity piston 26 of the first preferred embodiment ispreferably coupled to the displacement rod 24 and preferably extends tothe hydraulic tube 22. In this manner, the cavity piston 26 separatesthe inner cavity 30 into a first section 32 and a second section 34. Thecavity piston 26 defines a first orifice 36, which preferably betweenthe first section 32 and the second section 34 of the inner cavity 30.The first orifice 36 functions to allow flow of the compressible fluid20 between the first section 32 and the second section 34 of the innercavity 30. The cavity piston 26 is preferably securely mounted to thedisplacement rod 24 by a conventional fastener, but may alternativelyintegrally formed with the displacement rod 24 or securely mounted withany suitable device. The cavity piston 26 is preferably made fromconventional materials and with conventional methods, but mayalternatively be made from other suitable materials and with othersuitable methods.

[0014] The first variable restrictor 28 of the first preferredembodiment is coupled to the cavity piston 26 near the first orifice 36.The first variable restrictor 28 functions to restrict the passage ofthe compressible fluid 20 through the first orifice 36 and, morespecifically, functions to variably restrict the passage based on thevelocity of the cavity piston 26 relative to the hydraulic tube 22. Inthe first preferred embodiment, the first variable restrictor 28 is afirst shim stack 38 preferably made from conventional materials and withconventional methods. In alternative embodiments, the first variablerestrictor 28 may include any other suitable device able to variablyrestrict the passage of the compressible fluid 20 through the firstorifice 36 based on the velocity of the cavity piston 26 relative to thehydraulic tube 22.

[0015] In the first preferred embodiment of the invention, the cavitypiston 26 also defines a second orifice 40, which—like the first orifice36—preferably extends between the first section 32 and the secondsection 34 of the inner cavity 30 and functions to allow flow of thecompressible fluid 20 between the first section 32 and the secondsection 34 of the inner cavity 30. Further, the suspension strut 10 ofthe first preferred embodiment also includes a second variablerestrictor 41 coupled to the cavity piston 26 near the second orifice40. The second variable restrictor 41—like the first variable restrictor28—functions to restrict the passage of the compressible fluid 20through the second orifice 40 and, more specifically, functions tovariably restrict the passage based on the velocity of the cavity piston26 relative to the hydraulic tube 22.

[0016] In the preferred embodiment, the second variable restrictor 41 isa second shim stack 42 preferably made from conventional materials andwith conventional methods. In alternative embodiments, the secondvariable restrictor may include any suitable device able to variablyrestrict a passage of the compressible fluid 20 through the secondorifice 40 based on the velocity of the cavity piston 26 relative to thehydraulic tube 22.

[0017] The cavity piston 26, the first orifice 36, and the firstvariable restrictor 28 of the first preferred embodiment cooperate tosupply the rebound damping force during the rebound movement of thewheel. The rebound damping force acts to dampen the suspending springforce that tends to push the displacement rod 24 out of the hydraulictube 22. The cavity piston 26, the second orifice 40, and a secondvariable restrictor 41, on the other hand, cooperate to supply thecompression damping force during the compression movement of the wheel.The compression damping force acts to dampen any impact force that tendsto push the displacement rod 24 into the,hydraulic tube 22.

[0018] The hydraulic tube 22 of the first preferred embodiment includesa first portion 44 and a second portion 46, which aids in the assemblyof the suspension strut 10. During the assembly, the second portion 46of the hydraulic tube 22 is slid over the displacement rod 24 and thecavity piston 26 is mounted to the displacement rod 24, preferably witha fastener. Then, the cavity piston 26 is slid into the first portion 44of the hydraulic tube 22 and the second portion 46 of the hydraulic tube22 is fastened to the first portion 44, preferably with a weld. Thesuspension strut 10 of the first preferred embodiment also includesbearings and seals between the sliding elements of the suspension strut10.

[0019] As shown in FIGS. 1 and 2, the suspension strut 10 of the firstpreferred embodiment also includes a first connector 47A and a secondconnector 47B. In the preferred embodiment, the connectors 47A and 47Bare made from a structural material that firmly mounts the suspensionstrut 10 to the vehicle 12 without any substantial compliancy. In thismanner, the suspension strut 10 provides all of the isolation betweenthe vehicle 12 and the suspension link 18. In alternative embodiments,either the first connector 47A, the second connector 47B, or bothconnectors 47A and 47B may include elastic material that connects thesuspension strut 10 to the vehicle 12 with some compliancy. In thismanner, the suspension strut 10 and the connectors 47A and 47B act in aseries to provide the isolation between the vehicle 12 and thesuspension link 18. The connectors 47A and 47B are preferably made withconventional materials and from conventional methods, but mayalternatively be made with any suitable material and from any suitablemethod.

[0020] As shown in FIG. 3, in addition to the components of thesuspension strut 10 of the first preferred embodiment, the suspensionstrut 10′ of the second preferred embodiment includes a pressure vessel48. The pressure vessel 48 cooperates with a modified hydraulic tube 22′to define an outer cavity 50 located between hydraulic tube 22′ and thepressure vessel 48. The hydraulic tube 22′ defines a tube opening 52,which functions to fluidly connect the first section 32 of the innercavity 30 and the outer cavity 50. Effectively, the presence of the tubeopening 52 within the hydraulic tube 22 and the pressure vessel 48around the hydraulic tube 22′ greatly expands the volume of compressiblefluid 20 on the “compression side” of the cavity piston 26′. In thismanner, the size of the hydraulic tube 22′ and the size of the pressurevessel 48 may be adjusted to optimize the suspending spring force of thesuspension strut 10′. In an alternative embodiment, the hydraulic tube22′ may define a tube opening to fluidly connect the second section 34of the inner cavity 30 and the outer cavity 50 which would greatlyexpand the volume of compressible fluid 20 on the “rebound side” of thecavity piston 26′. In all other aspects, the suspension strut 10′ of thesecond preferred embodiment is similar to the suspension strut 10 of thefirst preferred embodiment.

[0021] As shown in FIG. 4, in addition to the components of thesuspension strut 10′ of the second preferred embodiment, the suspensionstrut 10″ of the third preferred embodiment includes a controllablevalve 54 near the tube opening 52 of the hydraulic tube 22′. Thecontrollable valve 54 functions to selectively restrict passage of thecompressible fluid 20 between the first section 32 of the inner cavity30 and the outer cavity 50. The presence or absence of the connectionbetween the first section 32 of the inner cavity 30 and the outer cavity50 dramatically affects the suspending spring force of the suspensionstrut 10″.

[0022] The suspension strut 10″ of the third preferred embodiment alsopreferably includes an electric control unit (not shown) coupled to thecontrollable valve 54. The electric control unit functions toselectively activate the controllable valve 54. Because selectiveactivation of the controllable valve 54 dramatically affects volume ofthe compressible fluid 20 on the “compression side” of the cavity piston26′, the electric control unit can actively modulate the suspendingspring force, the rebound damping force, and the compression dampingforce to achieve the desired ride and handling for the vehicle. Forexample, as the vehicle encounters a harsh impact force, or a fast turn,the electric control unit may close the controllable valve 54 therebydecreasing the volume of the compressible fluid 20 on the “compressionside” of the cavity piston 26′. This response may achieve the desiredride and handling for the vehicle. Both the controllable valve 54 andthe electric control unit are preferably conventional devices, but mayalternatively be any suitable device to selectively restrict the passageof compressible fluid.

[0023] As any person skilled in the art of suspension struts willrecognize from the previous description and from the figures and claims,modifications and changes can be made to the three preferred embodimentof the invention without departing from the scope of this inventiondefined in the following claims.

We claim:
 1. A suspension strut for a vehicle having a wheel contactinga surface under the vehicle and a suspension link suspending the wheelfrom the vehicle and allowing compression movement of the wheel towardthe vehicle and rebound movement of the wheel toward the surface, saidsuspension strut comprising: a compressible fluid; a hydraulic tube anddisplacement rod adapted to couple the suspension link and the vehicle,said hydraulic tube defining an inner cavity adapted to contain aportion of said compressible fluid and to cooperate with saidcompressible fluid to supply a suspending spring force that biases thewheel toward the surface, said displacement rod adapted to move intosaid inner cavity upon the compression movement of the wheel and to moveout of said inner cavity upon the rebound movement of the wheel; acavity piston coupled to said displacement rod and extending to saidhydraulic tube thereby separating said inner cavity into a first sectionand a second section, said cavity piston defining a first orificeadapted to allow flow of said compressible fluid between said firstsection and said second section of said inner cavity; and a firstvariable restrictor coupled to said cavity piston and adapted tovariably restrict the passage of said compressible fluid through saidfirst orifice based on the velocity of said cavity piston relative tosaid hydraulic tube; wherein said cavity piston, said first orifice, andsaid first variable restrictor cooperate to supply a rebound dampingforce during the rebound movement of the wheel.
 2. The suspension strutof claim 1 wherein said compressible fluid includes a silicone fluid. 3.The suspension strut of claim 1 wherein said compressible fluid has alarger compressibility above 2,000 psi than hydraulic oil.
 4. Thesuspension strut of claim 1 wherein said compressible fluid is adaptedto compress about 1.5% volume at 2,000 psi, about 3% volume at 5,000psi, and about 6% volume at 10,000 psi.
 5. The suspension strut of claim1 wherein said first variable restrictor is a first shim stack.
 6. Thesuspension strut of claim 1 wherein said cavity piston defines a secondorifice adapted to allow passage of said compressible fluid between saidfirst section and said second section of said inner cavity.
 7. Thesuspension strut of claim 6 further comprising a second variablerestrictor coupled to said cavity piston and adapted to variablyrestrict the passage of said compressible fluid through said secondorifice based on the velocity of said cavity piston relative to saidhydraulic tube.
 8. The suspension strut of claim 7 wherein said cavitypiston, said second orifice, and said second variable restrictorcooperate to supply a compression damping force during the compressionmovement of the wheel.
 9. The suspension strut of claim 8 wherein saidsecond variable restrictor is a second shim stack.
 10. The suspensionstrut of claim 1 further comprising a pressure vessel defining an outercavity located between said pressure vessel and said hydraulic tube andadapted to contain a portion of said compressible fluid; wherein saidhydraulic tube defines a tube opening adapted to fluidly connect saidfirst section of said inner cavity and said outer cavity; and whereinsaid pressure vessel and said tube opening cooperate with said hydraulictube and said compressible fluid to supply the suspending spring force.11. The suspension strut of claim 10 further comprising a controllablevalve adapted to selectively restrict passage of said compressible fluidbetween said first section of said inner cavity and said outer cavity.12. The suspension strut of claim 11 further comprising an electriccontrol unit adapted to selectively activate said controllable valve,thereby actively modulating the suspending spring force.
 13. Thesuspension strut of claim 11 wherein said electric control unit isfurther adapted to selectively actuate said controllable valve, therebyactively modulating the rebound damping force.
 14. The suspension strutof claim 11 wherein said electric control unit is further adapted toselectively actuate said controllable valve, thereby actively modulatingthe compression damping force.
 15. The suspension strut of claim 1further comprising a connector adapted to pivotally mount saidsuspension strut to the vehicle without substantial compliancy.